Fuel tank inerting system

ABSTRACT

A fuel tank inerting system in which the tank ullage contains a non-combustible gaseous mixture of fuel vapor, oxygen and an inert gas, such mixture from the ullage being circulated through incoming liquid fuel when the tank is being filled for scrubbing dissolved oxygen from the fuel and diluting the same as it rises to the tank ullage, and there being a means for introducing a fresh supply of inert gas from a separate source for continuing the scrubbing and diluting of oxygen from the incoming fuel only when the oxygen content of the tank ullage nears a predetermined yet non-combustible percentage, whereby a minimum amount of fresh inert gas is utilized for maintaining the ullage gases incombustible during filling of the tank and during subsequent ascending flight of the aircraft.

United States Patent Hickey et a1.

[ 51 Sept. 19, 1972 [54] FUEL TANK INERTING SYSTEM [72] Inventors:William G. Hickey, Corona Del Mar; Richard L. Kenyon, Costa Mesa, bothof Calif.

[73] Assignee: Parker-Hannifin Corporation,

Cleveland, Ohio [22] Filed: May 18, 1971 [21] Appl. No.: 144,589

[52] U.S. Cl ..55/166, 55/196, 220/88 B, 244/135, 261/77, 261/121 [51]Int. Cl. ..B0ld 19/00 [58] Field of Search ..55/18, 21, 47, 53, 159,160,55/166, 196, 199; 220/88 13; 244/135; 261/77, 121

[56] References Cited UNITED STATES PATENTS 2,870,936 1/1959 Clayton..220/88 B 3,229,446 l/ 1966 Sebastien et a1 ..55/53 3,590,559 7/1971Bragg ..55/21 X 3,628,758 12/1971 Nichols ..55/53 X PrimaryExaminerReuben Friedman Assistant Examiner-R. W. Bruks Attorney-John N.Wolfram ABSTRACT A fuel tank inerting system in which the tank ullagecontains a non-combustible gaseous mixture of fuel vapor, oxygen and aninert gas, such mixture from the ullage being circulated throughincoming liquid fuel when the tank is being filled for scrubbingdissolved oxygen from the fuel and diluting the same as it rises to thetank ullage, and there being a means for introducing a fresh supply ofinert gas from a separate source for continuing the scrubbing anddiluting of oxygen from the incoming fuel only when the oxygen contentof the tank ullage nears a predetermined yet non-combustible percentage,whereby a minimum amount of fresh inert gas is utilized for maintainingthe ullage gases incombustible during filling of the tank and duringsubsequent ascending flight of the aircraft.-

18 Claims, 3 Drawing Figures FUEL TANK INERTING SYSTEM BACKGROUND OF THEINVENTION A mixture of air, which contains about 23 percent oxygen, withfuel vapor in the ullage of an aircraft fuel tank is highly combustible.To render the fuel vapor and air mixture incombustible it has heretoforebeen proposed to introduce an inert gas such as nitrogen into the tankullage so as to reduce the oxygen content to about 10 percent or less,the exact percentage depending upon the particular conditions ofpressure and temperature.

Liquid fuel in an aircraft tank at ground level atmospheric pressurenormally contains oxygen dissolved therein in proportion to the groundlevel partial pressure of the oxygen in ambient air; As the aircraftascends, oxygen is released from the liquid fuel into the tank ullage aspressure in the tank is decreased in accordance with the decrease inambient pressure. At operating altitudes for jet aircraft enough oxygenwill have been released from the fuel so thatthe oxygen content in theullage would be about twice that when the aircraft is on the ground.Thus, even though the oxygen content of the ullage is l percent or lesswhile the aircraft is on the ground, to maintain this percentage atoperating altitude it is necessary to either add nitrogen as theaircraft ascends or to reduce the oxygen concentration in the tank toabout percent or less (preferably about 4.5 percent which provides somesafety factor) while the aircraft is on the ground.

Although nitrogen must be carried on board for pressurizing the aircrafttank during descent if the ullage gases are to be maintained in anon-combustible mixture, utilization of nitrogen during ascent forscrubbing and diluting dissolved oxygen from the fuel, as disclosed, forexample, in U.S. Pat. application, Ser. No. 711,020, now U.S. Pat. No.3,590,559, requires not only a larger capacity dewar to be installed inthe aircraft but also entails installation in the aircraft ofsophisticated equipment for distributing and controlling the flow of thenitrogen to the tank during ascent.

On method of removing oxygen from fuel while the aircraft tank is beingfilled on the ground is disclosed in U.S. Pat. No. 3,229,446. In thismethod sufficient nitrogen may be introduced from a source on the groundexternal of the aircraft for scrubbing and diluting the oxygen from theincoming fuel as the tank is being filled so that when the tank is fullthe oxygen concentration in the ullage is about 4.5 percent or less.Because a rather large quantity of nitrogen must be vented to atmospherealong with oxygen and fuel vapor as the tank is being filled, the amountof nitrogen utilized by this method is considerable.

SUMMARY OF THE INVENTION The disadvantages of the above describedmethods of introducing nitrogen either during ascent of the aircraft oron the ground during filling of the tank are overcome in the presentinvention by providing a system in which nitrogen already in the tankfrom a previous inerting operation is utilized for scrubbing anddiluting oxygen from the fuel during the first part of a tank fillingoperation and by adding fresh nitrogen from a separate source only whenthe oxygen concentration in the ullage approaches 4.5 percent. In thismanner the necessity for adding nitrogen to the tank during ascent ofthe aircraft is avoided and a minimum amount of nitrogen is used duringthe tank filling operation on the ground.

At sea level a fuel tank containing little or no fuel but containingfuel vapor and nitrogen gas that has been added to the tank topressurize the same during descent of the aircraft will contain aslittle as 0.5 percent of oxygen. If this ullage gaseous mixture isutilized for removing oxygen from incoming fuel as the tank is beingrefueled, the oxygen content of the ullage will gradually increase andwill be about 4.5 percent when the tank is about 55 percent full. Thepresent invention provides for utilizing the. ullage gases for thispurpose and when the tank is about 55 percent full and the ullage oxygencontent is about 4.5 percent the use of the ullage gases for thispurpose is discontinued and fresh nitrogen either from a dewar in theaircraft or from a separate supply on the ground is cut in to continuethe scrubbing and diluting function with enough fresh nitrogen beingused to keep the ullage oxygen content to 4.5 percent or less. This isaccomplished in one form of the invention by drawing the ullage gasesinto the incoming stream of liquid fuel by means of a tube leading fromthe ullage to an aspirating nozzle in the fuel supply line andautomatically closing the tube and cutting in a separate supply of purenitrogen'when the tank is filled to about 55 percent of its capacity.

Closing of the tube is accomplished either by way of a float operatedvalve or by an electrically actuated valve controlled by a floatoperated switch. Cutting in of the separate nitrogen supply issimultaneously accomplished either by a pressure differential responsivevalve actuated by lowering of pressure in the tube when the valve in thelatter closes, or by an electrically operated valve actuated by theaforementioned float switch.

In another form of the invention the separate source of nitrogen is cutin without discontinuing utilization of the ullage nitrogen. In suchcaseoptimum utilization of nitrogen occurs if the separate source is cutin when the tank is from about 30 percent to 50 percent full, dependingupon relative flow rates of the ullage nitrogen and fresh nitrogen, aswell as other factors.

Thus, in its broadest aspects, the invention provides for mixing ofinert ullage gases with incoming liquid fuel for removing oxygen fromthe latter, and utilizing a separate source of inert gas to augment theuse of inert ullage gases only to the extent necessary to have theoxygen content of the ullage at a predetermined percentage when the tankhas been filled with liquid fuel.

DETAILED DESCRIPTION FIG. 1 is a schematic view of one form of theinvention in which ullage gases are cut off by a float operated valve ata predetermined fuel level and a pressure differential device isthereupon actuated for cutting in a separate source of nitrogen.

FIG. 2 is a schematic view of a modified form of the invention in whichullage gases" are not cut off and a float operated switch actuates anelectric valve for cutting in the separate nitrogen supply at apredetermined level of fill.

FIG. 3 is a schematic partial view of another form of the invention inwhich a float operated switch actuates one electric valve to discontinueutilization of ullage gases and actuates another electrically operatedvalve to open the separate nitrogen supply when the fuel in the tank hasreached a-predetermined level.

In FIG. 1, aircraft fuel tank has mounted therein an aspirating nozzle11 having an opening 12 to the tank and having an inlet conduit 13connected to a conventional fluid pressure operated level control valve14 attached to the wall of tank 10 and controlled via pilot line 22 by afloat operated pilot valve 15. A filling nozzle 16 may be connected tovalve 14 by means of a rotatable connector sleeve 17 operable by handles18. Nozzle 16 may, for example, be like that shown in U.S. Pat. No.2,630,822 and valve 14 and its float valve may be as shown in U.S. Pat.No. 3,01 1,752. A pump P has its inlet 20 connected to the interior of asupply tank 21 containing liquid fuel. The discharge side of pump P isconnected by means of a hose or other con duit 23 to a conventionalnozzle 15 having a valve therein openable by turning'of a handle 24after the nozzle is connected to valve 14.

Leading from aspirator ll is a vertically disposed conduit 26. A valveelement 27 is pivotally mounted at 28 on the upper end of conduit 26 andhas attached thereto a float element 29, conduit 26 being of such lengththat float-29 will operate to cause valve 27 to close its upper end whenliquid fuel has filled the tank to a predetermined level. Suchpredetermined level for the form of invention shown in FlG. 1 ispreferably such that the tank will be filled no more than about 55% whenvalve 27 closes conduit 26.

Branching from conduit 26 is another conduit 31 which is connected to adewar 32 carried in the aircraft, and containing liquid nitrogen.Alternately, conduit 32 may be connected to a separate dewar (not shown)that is on the ground. Conduit 31 may contain a heat exchanger 34 toassure that the liquid nitrogen will be delivered to conduit 26 in agaseous state.

Contained in conduit 31 is a shut-off valve 38. Connected to valve 38 isa pressure differential device 39 having a diaphragm 40 connected by arod 41 to valve 38 and whose upper side is vented to tank via a port 42and whose lower side is exposed to pressure in conduit 31 via sensingline 43.

Mounted at the upper end of tank 10 is a nozzle 49 connected by aconduit 50 to dewar 32 by branch conduit 50 in which is installed ashut-ofl valve 53 controlled by a pressure differential device 54 thatsenses pressure within tank 10 and ambient pressure externally of tank10. Device 54 actuates valve 53 to closed position when tank pressureexceeds ambient pressure by a predetermined amount, such as 0.5 psi forexample, and causes valve 53 to open when tank pressure exceeds ambientpressure by less than such predetermined amount. If conduit 31 isconnected to a dewar on the ground, dewar 32 is nevertheless provided inthe aircraft and conduit 50 is connected to the same so that nitrogenmay be utilized for pressurizing the tank during descent of theaircraft.

At the upper end of tank 10 is a climb valve 56 that opens to vent theinterior of tank 10 to atmosphere when tank pressure exceeds ambientpressure by a predetermined amount, such as 0.5 psi for example. Thereis also a dive valve 56 that opens under emergency conditions whenambient pressure exceeds the tank pressure by an amount slightly morethan the differential at which valve 51 opens.

After an aircraft having a fuel tank 10 fitted with the system shown inFIG. 1 is on the ground with tank 10 empty or only partly full of liquidfuel, the tank ullage will contain a mixture of fuel vapor, oxygen andnitrogen. Because nitrogen is added to the tank from dewar 32 forpressurizing the tank during descent of the aircraft, the oxygen contentwill be materially less than 4.5 percent and may be as low as 0.5percent. Preparatory to filling of the tank with liquid fuel, nozzle 16is connected to valve 14 and handle 24 is rotated to open the valvewithin nozzle 16. At this time, floats 29 and 19 will be at theirlowermost positions by action of gravity and hold valve 27 and 15 intheir open posiemergence of the gaseous mixture with the additionalentrained oxygen from aspirator opening 12, the gaseous mixture risesthrough the liquid fuel to the tank ullage. As the ullage gases keepcirculating through conduit 26 and aspirator 11 in this manner, theoxygen content gradually increases as the tank is being filled. As theliquid level rises, the pressure in the tank also tends to rise and willcause valve 55 to open and vent ullage gases to atmosphere to preventthe tank pressure from exceeding ambient pressure by more than thepredetermined amount. The vented gases, which include nitrogen, arenormally not collected and are lost.

By the time the liquid level has reached the point where the tank isabout 55 percent full, the oxygen content of the ullage gases hasreached about 4.5 percent and at this point float 29 is lifted by theliquid and actuates valve 27 to a position for closing conduit 26, thuscutting off further circulation of ullage gases through aspirator 11.Closing of valve 27 causes aspirator 11 to reduce the pressure withinconduit 26 by an additional amount. This also reduces the pressure inconduit 31 and the lower side of diaphragm 40 via sensing lines 43, 44so that diaphragm 40 and rod 41 move downward to open valve 38. Thispermits flow of pure nitrogen from dewar 48 into conduit 26 andaspirator 11 for continuing the action of scrubbing dissolved oxygenfrom the liquid fuel flowing through aspirator 11 into tank 10 and addsnitrogen to the tank ullage for maintaining the oxygen content thereinat 4.5 percent or less while filling of the tank is completed. When thetank is full, float 19 will close valve 15 which in turn causes valve 14to close and discontinue flow of fuel into the tank. This causespressure in conduit 26 to increase until it is equalized with tankpressure. Diaphragm 40 then closes valve 38 to shut off flow of nitrogeninto the tank.;l-landle 24 may now be turned for closing the valve innozzle 16 and the latter may be disconnected from valve 14. The aircraftis now ready for flight.

As the aircraft climbs, ambient pressure decreases and climb valve 55opens to vent ullage gases from tank 10 so that tank pressure will notexceed ambient by more than the predetermined amount. When tank pressuredecreases because of consumption of fuel at operating altitude, and alsowhen tank pressure must be increased during descent, differentialpressure device 54 causes valve 53 to open for admitting nitrogen fromdewar 32 through nozzle 49 to pressurize the tank so as to maintain the.proper differential with respect to ambient pressure. Dive valve 56opens for admitting air to the tank only in those emergency situationswhere valve 53 for some reason fails to open or where the supply ofnitrogen in dewar 32 has been unexpectedly exhausted.

Upon emptying or partial emptying of tank and the return of the aircraftto the ground, the ullage of tank 10 will contain a mixture of fuelvapor, oxygen and nitrogen in which the oxygen content will beconsiderably less than 4.5 percent and the tank again will be ready forfilling in a manner to utilize the nitrogen therein for scrubbing oxygenfrom incoming fuel and to cut in the separate supply of nitrogen fromonly when the tank is again filled to the predetermined level, as abovedescribed.

In the form of the invention shown in FIG. 2, conduit 26 extends to aposition near the top of the tank and normally closed electricallyoperated valve 60 and float operated switch 61 replace differentialpressure valve 38 and float operated valve 27 of FIG. 1, respectively.Sensing line 43 is omitted and conduit 64 connected to the outlet sideof valve 60 enters conduit 26 and has its inner end directed downwardlyas shown. Float 19 when in its lowered position closes a switch 67 inseries with switch 61 while the tank is not full of liquid fuel andopens switch 67 when the tank is full. Another switch 70 in the powersupply line may be closed and opened before and after the fuelingoperation either manually or automatically in conjunction with operationof fueling pump P or the plugging and unplugging of the groundingconnections for the fueling equipment. Opening of switch 70 in thismanner after fueling has been discontinued permits valve 60 to remainclosed when fuel level during flight drops enough to permit float 19 toclose switch 67 but not enough to open switch 61.

In this arrangement, when fuel is pumped through conduits 23 and 13through aspirator l1 and into tank 10 while the fuel is below apredetermined level in the tank, ullage gases will be drawn into theupper end of tube 26 and into aspirator 1 1 to scrub dissolved oxygenfrom fuel passing through the aspirator in the same manner as describedin connection with FIG. 1. When the fuel reaches the predetermined levelin the tank, float switch 61 will be closed to energize and actuatevalve 60 from a normal spring closed position to an open position foradmitting pure nitrogen from dewar 32 through conduit 31 into conduit 26where it will mix with ullage gases being drawn into conduit 26 and passinto aspirator 11 for scrubbing oxygen from liquid fuel passingtherethrough. As with FIG. 1, ullage gases will vent through valve 55during the filling operation and the feed of pure nitrogen from dewar 32is so adjusted that the oxygen content of the ullage gases will be about4.5 percent when the tank is full. Also, when the tank is full switch 67is opened by float 19 to cause valve 60 to close for shutting off flowof nitrogen into the tank via conduit 31.

The arrangement of FIG. 3 is similar to that of FIG. 2 except that floatoperated switch 61 when closed also actuates a normally open electricvalve 65 for closing the upper end of conduit 26 at the same time thatthe switch operates valve 60 to open position. Thus, in this arrangementconduit 26 is closed off when the tank is partially filled to preventfurther circulation of ullage gases through aspirator 11 and in thisrespect is similar to FIG. 1. When the tank is full of fuel floatoperated switch 67 opens causing valve 65 to revert to its normally openposition and valve 60 to its normally closed position. Also, switch 70is opened and closed at the beginning and end of the tank fillingoperation for the same purpose and as described in connection with FIG.2

For all forms of the invention disclosed herein means have beendescribed for shutting off flow of fuel and nitrogen to the tank whenthe tank is full of fuel. Shut off of these fluids can also beaccomplished when the tank is only partially filled. For example, pump Pis usually driven by an electric motor and the controls for the samecommonly include a means for'shutting off the motor and pump when aselected quantity of fuel is delivered to the tank. In the FIG. 1 form,such shutting off of fuel flow will automatically result in closing ofvalve 38, as already described. For FIGS. 2 and 3, a relay may beprovided in the electric circuit for the motor for pump P for actuatingswitch 70 to closed position when pump P is turned on and to openposition when the pump is turned off. In such case, valve 15 and switch67 serve as safety devices for shutting off fuel and nitrogen flow whenthe tank is full of fuel in the event pump P has failed to shut off.

I claim:

1. An inerting system comprising a fuel tank whose ullage contains asufficient supply of inert gas whereby the oxygen content of the ullageis below an amount that would support combustion of fuel vapor therein,a separate supply of inert fluid connected to the tank,

first means for introducing liquid fuel into the tank for filling thesame, second means for mixing said inert ullage gas with said incomingfuel to remove oxygen from the fuel, and third means for automaticallyinitiating flow of said inert fluid to said tank when a predeterminedamount of liquid fuel has been supplied to the tank.

2. The system of claim 1 in which there is a means for automaticallystopping flow of said inert fluid to the tank when the latter is full offuel.

3. The system of claim 1 in which said second means includes a valvecontrolled conduit connecting the ullage with the incoming liquid fueland there is a fourth means that automatically causes the valve to closewhen a predetermined amount of liquid fuel has entered the tank.

4. The system of claim 1 in which said third means is automaticallyactuated by a float operated device to permit flow of said inert fluidinto the tank when the liquid fuel has reached a predetermined level inthe tank.

5. The system of claim 1 in which there is a means for automaticallydiscontinuing flow of said inert fluid to the tank when flow of liquidfuel to the tank is discontinued.

6. The system of claim 1 in which there are means for automaticallyshuttingoff flow of incoming liquid fuel and flow of said inert fluidinto the tank when the tank is substantially full of liquid fuel.

7'. An inerting system comprising a fuel tank containing an inert gas inits ullage, first means including a first conduit for delivering liquidfuel from a supply source to said tank for filling the latter with theliquid fuel, second means including a second conduit for deliveringinert fluid to the tank from a source other than the tank ullage, athird conduit connecting the ullage to the first conduit, and thirdmeans responsive to a predetermined level of liquid fuel in the tank foropening the second conduit.

8. The system of claim 7 in which said third means includes a valveactuated by a float operated device responsive to said predeterminedlevel to cause closing of said third conduit.

9. The system of claim 7 in which said third means includes a floatoperated valve that closes the third conduit at said predeterminedlevel.

10. The system of claim 7 in which said first conduit includes anaspirator and said third conduit is connected to the aspirator.

1 l. The system of claim 7 in which said second conduit is alsoconnected to said aspirator.

12. The system of claim 1 l in which said second conduit is connected tothe aspirator via said third conduit.

13. The system of claim 7 in which said third means includes a floatoperated switch responsive tosaid predetermined level to cause openingof said second conduit and which also causes closing of said thirdconduit.

14. The system of claim 7 in which said third means is actuated upon thetank becoming filled to about 55 percent of its capacity.

15. The system of claim 8 in which there is a normally closed valve insaid second conduit, means causing a lowering of fluid pressure withinsaid third conduit when said float actuated valve closes, and there is apressure differential operated device responsive to said lowering offluid pressure in said third conduit for opening said normally closedvalve.

16. The system of claim 7 in which said third conduit is always open toan upper region of the tank.

17. The system of claim 7 in which there is a supply of inert fluid inthe aircraft connected by a fourth conduit to the tank, and there is ameans actuated by a predetermined differential in pressure between theinterior and exterior of the tank for opening the fourth conduit forintroducing inert fluid from said supply in the aircraft to the tankwhen the aircraft descends in altitude.

18. The system of claim 7 in which there are automatically operatedmeans for closing off both the supply of liquid fuel and inert fluidwhen the tank is substantially full.

1. An inerting system comprising a fuel tank whose ullage contains asufficient supply of inert gas whereby the oxygen content of the ullageis below an amount that would support combustion of fuel vapor therein,a separate supply of inert fluid connected to the tank, first means forintroducing liquid fuel into the tank for filling the same, second meansfor mixing said inert ullage gas with said incoming fuel to removeoxygen from the fuel, and third means for automatically initiating flowof said inert fluid to said tank when a predetermined amount of liquidfuel has been supplied to the tank.
 2. The system of claim 1 in whichthere is a means for automatically stopping flow of said inert fluid tothe tank when the latter is full of fuel.
 3. The system of claim 1 inwhich said second means includes a valve controlled conduit connectingthe ullage with the incoming liquid fuel and there is a fourth meansthat automatically causes the valve to close when a predetermined amountof liquid fuel has entered the tank.
 4. The system of claim 1 in whichsaid third means is automatically actuated by a float operated device topermit flow of said inert fluid into the tank when the liquid fuel hasreached a predetermined level in the tank.
 5. The system of claim 1 inwhich there is a means for automatically discontinuing flow of saidinert fluid to the tank when flow of liquid fuel to the tank isdiscontinued.
 6. The system of claim 1 in which there are means forautomatically shutting off flow of incoming liquid fuel and flow of saidinert fluid into the tank when the tank is substantially full of liquidfuel.
 7. An inerting system comprising a fuel tank containing an inertgas in its ullage, first means including a first conduit for deliveringliquid fuel from a supply source to said tank for filling the latterwith the liquid fuel, second means including a second conduit fordelivering inert fluid to the tank from a source other than the tankullage, a third conduit connecting the ullage to the first conduit, andthird means responsive to a predetermined level of liquid fuel in thetank for opening the second conduit.
 8. The system of claim 7 in whichsaid third means includes a valve actuated by a float operated deviceresponsive to said predetermined level to cause closing of said thirdconduit.
 9. The system of claim 7 in which said third means includes afloat operated valve that closes the third conduit at said predeterminedlevel.
 10. The system of claim 7 in which said first conduit includes anaspirator and said third conduit is connected to the aspirator.
 11. Thesystem of claim 7 in which said second conduit is also connected to saidaspirator.
 12. The system of claim 11 in which said second conduit isconnected to the aspirator via said third conduit.
 13. The system ofclaim 7 in which said third means includes a float operated switchresponsive to said predetermined level to cause opening of said secondconduit and which also causes closing of said third conduit.
 14. Thesystem of claim 7 in which said third means is actuated upon the tankbecoming filled to about 55 percent of its capacity.
 15. The system ofclaim 8 in which there is a normally closed valve in said secondconduit, means causing a lowering of fluid pressure within said thirdconduit when said float actuated valve closes, and there is a pressuredifferential operated device responsive to said lowering of fluidpressure in said third conduit for opening said normally closed valve.16. The system of claim 7 in which said third conduit is always open toan upper region of the tank.
 17. The system of claim 7 in which there isa supply of inert fluid in the aircraft connected by a fourth conduit toThe tank, and there is a means actuated by a predetermined differentialin pressure between the interior and exterior of the tank for openingthe fourth conduit for introducing inert fluid from said supply in theaircraft to the tank when the aircraft descends in altitude.
 18. Thesystem of claim 7 in which there are automatically operated means forclosing off both the supply of liquid fuel and inert fluid when the tankis substantially full.